Multiple GitGraph improvements: Exclude PR heads, Add branch/PR links, Show only certain branches, (#12766)

* Multiple GitGraph improvements.

Add backend support for excluding PRs, selecting branches and files.

Fix #10327

Signed-off-by: Andrew Thornton <art27@cantab.net>

* as per @silverwind

Signed-off-by: Andrew Thornton <art27@cantab.net>

* as per @silverwind

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Only show refs in dropdown we display on the graph

Signed-off-by: Andrew Thornton <art27@cantab.net>

* as per @silverwind

Signed-off-by: Andrew Thornton <art27@cantab.net>

* use flexbox for ui header

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Move Hide Pull Request button to the dropdown

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Add SHA and user pictures

Signed-off-by: Andrew Thornton <art27@cantab.net>

* fix test

Signed-off-by: Andrew Thornton <art27@cantab.net>

* fix test 2

Signed-off-by: Andrew Thornton <art27@cantab.net>

* fixes

* async

* more tweaks

* use tabs in tmpl

Signed-off-by: Andrew Thornton <art27@cantab.net>

* remove commented thing

Signed-off-by: Andrew Thornton <art27@cantab.net>

* fix linting

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Update web_src/js/features/gitgraph.js

Co-authored-by: silverwind <me@silverwind.io>

* graph tweaks

* more tweaks

* add title

Signed-off-by: Andrew Thornton <art27@cantab.net>

* fix loading indicator z-index and position

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lauris BH <lauris@nix.lv>

web_src/less/_base.less

@@ -1391,6 +1391,10 @@ table th[data-sortt-desc] {
   }
 }
 
+.dropdown .ui.label {
+  margin-left: 0 !important;
+}
+
 .ui.dropdown .menu .item {
   border-radius: 0;
 }